Slack

Send and manage Slack messages, channels, reactions, users and files, pause a workflow until someone clicks a button, and start workflows from Slack in real time.

Connecting

Flero-managed sign-in

Click Sign in with Slack in a Slack node and approve the app in your Slack workspace. Flero's app asks for these bot scopes:

chat:write, chat:write.public, channels:read, groups:read, im:read, mpim:read, channels:history, groups:history, im:history, mpim:history, channels:manage, groups:write, users:read, usergroups:read, reactions:read, reactions:write, files:read, files:write

This is enough for every Slack action. It does not support the real-time triggers.

Your company's own Slack app

Real-time triggers need a Slack app that belongs to your Slack workspace, because Slack sends every event for an app to one URL, and that URL must point at your Flero instance. Flero creates the app for you from a template.

An organization admin does this once:

1. Open a Slack Trigger node and click Add Flero to Slack.
2. At api.slack.com/apps, under "Your App Configuration Tokens", create a configuration token and paste it. Optionally paste the refresh token too, so Flero can keep the token fresh. Choose the app name.
3. Review the permissions. The recommended ones are ticked. Untick any the app should not have. Flero drops the Slack events and the slash command that the remaining permissions no longer cover.
4. Click Create app, then Install to Slack, and allow the requested scopes.
5. Wait for Slack to verify the events URL. If it stays pending, open the app's Event Subscriptions page from the link and click Verify.

Besides the managed app's scopes, the template can request commands, im:write, users:read.email, app_mentions:read, metadata.message:read and channels:join.

The configuration token is used once and not stored. The new credential works for both the Slack node and the Slack Trigger. Other users see the button greyed out with a note about who can complete the step. Once the app exists, everyone sees "Flero is connected to Slack".

Your Flero address must be reachable from the internet for Slack to deliver events.

To change the app's permissions later, run Set up again. This creates a second Slack app.

Bot token

You can also paste a bot token (xoxb-…) from a Slack app you manage yourself. It works for actions only.

Operations

Channel and user fields are dropdowns filled from your Slack workspace. The posted message's timestamp is on {{ $node["Post summary"].output.data.ts }}.

Message layout

Send and Update have a Message layout field: an ordered list of blocks that Flero renders as Slack Block Kit. The Text field stays required. Slack shows it in notifications and wherever blocks cannot render.

Add items from the menu and reorder them with the arrows. The editor checks the layout as you go. A layout that is invalid at run time fails the node.

Button ids use a-z, 0-9, _ and -, up to 32 characters, unique within the message. They cannot be output, error or timeout. The Approve / Reject preset adds an approved and a rejected button, with the reject button collecting a comment.

Wait for response

Turn on Wait for response on Send or Update to pause the run until someone clicks a button, like an Approval in Slack. The Approve / Reject preset turns it on for you. The layout needs at least one button.

Both rules are checked. Neither needs a Flero account.

What happens:

• The node gets one output port per button, plus Timed out.
• A button that collects a comment, a person or a short form opens a Slack modal first. The decision is recorded when the person submits it. A picked person arrives as values.user, their Slack user ID.
• After a decision, the message is rewritten without buttons and with a line saying who decided and when. A later click gets a private "This request is no longer waiting for a response." note.
• The output on the chosen port has decision, label, timedOut, comment, values, actor, respondedAt, channel, ts, threadTs, text and responseUrl. For example, {{ $node["Ask for approval"].output.comment }}.

Turning the wait off does not delete connections from the old button ports. Remove them yourself.

Update the previous message

A toggle on Send. When the incoming data carries a Slack message ts (and a channel, if the node names none), Send edits that message instead of posting a new one. A review loop stays one message: draft, "Adjust by …", revised draft, approved text.

Reply privately, in place

A toggle on Send. The reply goes through the response URL from the slash command or button click that started the run. Only that person sees it, and each reply replaces the previous one. The node fails if the incoming data has no response URL. Slack limits how often a response URL can be used, so keep such loops short.

Triggers

All three Slack triggers are real-time and need your company's own Slack app. The trigger panel shows the events URL, whether the app is installed and verified, and the setup button when the credential is not a company app.

Public channels you pick are joined when the workflow is activated. Invite the app to private channels with /invite @<app name>.

• The app's own messages never trigger New message.
• Acknowledgement is the private reply Slack shows straight away. Unset, it reads "Flero is running /flero <text>". Set it to empty for silence.
• A slash command that no active workflow answers gets a private reply saying so, or saying the workflow is turned off.
• Read trigger fields from the node, for example {{ $node["Slack Trigger"].output.text }}. The person behind the event is on {{ $trigger.actor }}.

Known issue: the triggers show Who can start this and Who counts as allowed, but these are not enforced on triggers yet. They are enforced on Wait for response.

Limits

• Slack expects an answer within 3 seconds. Flero acknowledges first and works after. Slack's retries of the same event within 15 minutes are dropped.
• 50 blocks per message, 25 buttons, 3,000 characters per section, 12,000 per Markdown block. Flero enforces these and notes what it dropped.

Common errors

Related

• Approval basics
• Connector event triggers
• Recipe 01: Slack on webhook

Found something out of date? This page lives in the Flero docs content set.